Intrinsic loss of optical fibers

Rayleigh scattering is a dominant factor in terms of optical fiber loss. We investigated the dopant concentration and fictive temperature dependence of Rayleigh scattering in silica-based optical fibers and their glass preforms fabricated by the vapor-phase axial deposition (VAD) technique. The lowest Rayleigh scattering coefficient, which was obtained for a P2O5-doped silica preform, was about 80% of the pure silica value. In contrast, the Rayleigh scattering coefficients of F-doped and GeO2-doped and pure silica glass preforms increased by 5-10% when they were heated to 1800 °C because the density fluctuation is proportional to their fictive temperature. We also obtained very low Rayleigh scattering coefficients in fabricated fibers by controlling the preform composition or the fiber drawing conditions. We used these results to reevaluate the intrinsic losses of P2O5-doped, pure, and GeO2-doped silica core fibers and found them to be 0.095-0.130 dB/km at 1.55 μm by using the Rayleigh scattering coefficients of their preforms.